PowerBrightnessSync

Extreme Lightweight Windows Screen Brightness Sync Tool

PowerBrightnessSync is a background utility designed specifically for Windows. It monitors system Screen Brightness Changes, Display Power States, and Power Source (AC/DC) Switches, automatically synchronizing the current brightness value to all power schemes (both AC and DC settings).

It effectively solves the visual annoyance where Windows brightness suddenly "jumps" when plugging/unplugging the power cable, switching power modes, or waking the display.

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Core Features

Full Scenario Brightness Lock

Whether you are on battery or plugged in, once you adjust the brightness, this tool syncs the value to the "Plugged In" and "On Battery" settings of all existing power schemes. This ensures the brightness remains constant when you plug or unplug the charger.

️ Modern C++ & Robust Resource Management

Built with C++17 and native Win32 API.

• RAII & Smart Pointers: Uses Microsoft::WRL::ComPtr and std::unique_ptr with custom deleters to ensure zero memory leaks and safe handle management.
• COM Integration: Interacts directly with the Windows Task Scheduler via COM interfaces for reliable auto-start management.
• Tiny Footprint: Statically compiled into a single executable with no external dependencies.

Event-Driven & Zero Idle Load

Based on the WM_POWERBROADCAST event mechanism. The thread remains suspended and consumes 0% CPU until a brightness change, display toggle, or power source switch occurs.

️ Smart Debounce (600ms)

Includes a built-in 600ms debounce timer. When you slide the brightness bar, the tool waits for the operation to settle before writing to the registry/power config. This prevents spamming the system with write operations and protects your SSD.

Ghost Mode

Runs completely silently: No window, no tray icon, no console output. It uses a hidden Message-Only Window to process system events.

Single Instance Protection

Uses a named mutex (Local\PowerBrightnessSync_Mutex) to ensure only one instance is running at a time.

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Quick Start

System Requirements

• OS: Windows 10 / 11 (Recommended), Windows 7 SP1+
• Privileges: Administrator rights are mandatory.

⚠️ Why Administrator? Windows restricts modifying power schemes other than the "active" one by default. To prevent brightness jumps effectively, this tool must traverse and modify the AC/DC curves of all power schemes (including hidden ones), which requires elevated privileges.

How to Run

1. Download the latest PowerBrightnessSync.exe from Releases.
2. Right-click and select "Run as Administrator".
3. The program will perform an immediate sync and then enter background mode.
   • Note: You will not see any window. Check Task Manager for PowerBrightnessSync.exe to verify it is running.

How to Exit

Since there is no UI, use one of the following methods:

• Task Manager: Details tab -> End PowerBrightnessSync.exe.
• Command Line (Admin):

  taskkill /f /im PowerBrightnessSync.exe

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️ Auto-Start (Task Scheduler)

The program has built-in logic to manage Windows Task Scheduler. It creates a task with TASK_RUNLEVEL_HIGHEST to ensure it starts silently as Admin on login.

Argument	Description
--onar	ON Auto Run: Registers the scheduled task.
--ofar	OFF Auto Run: Removes the scheduled task.

Setup Example: Open CMD or PowerShell as Administrator:

:: Enable auto-start (A message box will confirm success)
PowerBrightnessSync.exe --onar

:: Disable auto-start
PowerBrightnessSync.exe --ofar

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️ AC / DC Brightness Behavior

• On Windows 10 (1903+) and Windows 11, AC (plugged in) and DC (battery) brightness are typically unified within the same power plan.
  Switching power sources usually does not change the brightness.

• In such cases, this program may not show noticeable effects — this is normal and does not indicate a malfunction.

• The tool is still useful for older Windows versions, certain OEM drivers, or devices where AC/DC brightness differs.
  Its main goal is to unify brightness across different power plans.

• Built using the official Windows Power Management API; behavior may vary depending on system version and hardware.

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️ Build Guide

If you wish to compile the source yourself:

Requirements:

• Visual Studio 2019 or later (MSVC)
• Windows SDK
• C++17 Standard support (Required for std::clamp and others)

Compilation Command: Open the x64 Native Tools Command Prompt for VS and run:

cl /nologo /W4 /EHsc /std:c++17 /O2 /MT /GL /DNDEBUG ^
/DUNICODE /D_UNICODE /D_WIN32_WINNT=0x0601 ^
PowerBrightnessSync.cpp ^
/link /LTCG /SUBSYSTEM:WINDOWS /OPT:REF /OPT:ICF ^
/MANIFEST:EMBED ^
/MANIFESTUAC:"level='requireAdministrator' uiAccess='false'" ^
/OUT:PowerBrightnessSync.exe

Build Notes:

• /std:c++17: Strictly required.
• /MT: Statically links the CRT, so the EXE runs on machines without VC++ Redistributables.
• #pragma comment: The source code automatically links PowrProf, User32, Advapi32, Kernel32, Shell32, taskschd, and comsupp, so you don't need to list .lib files manually.

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How It Works

1. Initialization:

   • Checks for Admin rights and Single Instance Mutex.
   • Creates a hidden window (HWND_MESSAGE).
   • Registers specifically for GUID_VIDEO_BRIGHTNESS and GUID_CONSOLE_DISPLAY_STATE notifications.

2. Event Loop:

   • Upon receiving WM_POWERBROADCAST, it resets a 600ms timer.
   • Once the timer expires (user stopped sliding brightness), the PerformSync() function is called.

3. Synchronization Logic (PerformSync):

   • Gets the active power scheme.
   • Reads the current effective brightness.
   • Iterates through every available power scheme on the system.
   • Writes the current brightness value to both the AC (Plugged In) and DC (Battery) indices for the Video Subgroup.

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Disclaimer

This tool modifies system power configuration (specifically brightness curves). While the code implements safety measures (RAII, bounds checking, debounce), behavior may vary depending on specific hardware drivers or OEM power management software.

Authors are not responsible for any system anomalies caused by the use of this tool.

If you encounter bugs, please submit an Issue.